1. Field of the Invention
This invention pertains to kilns used to dry wood, and more particularly kilns that used heat and a vacuum to dry wood.
2. Description of the Related Art
After the wood has kiln dried, the wood is lighter, easier to transport, stronger, contains fewer infestations, less susceptible to shrinkage, and easier to cut and stain.
Today, recently cut wood is pre-dried by being stacked in piles and ‘air dried’. During this stage, air that flows over the wood exposed surfaces and any free water located on the exposed surface and in the cells located adjacent to the surfaces to slow evaporated. Unfortunately, the pre-drying stage can be 1.5 to 5 months depended on the temperature and humidity. After the pre-drying stage have been completed, the moisture content of the wood is still relatively high, 25 to 33% (by weight).
To remove more water from the wood, the wood is placed in a kiln wherein hot air is circulated around the surfaces of the wood to evaporate more water. While the temperature of the wood may be increased a small amount which causes more evaporation, the moisture content of the wood is still between 6-19% (by weight).
Unfortunately, the kiln drying process that relies on hot air circulated over the exposed surface of wood is energy inefficient and causes substantial damage to the wood itself. Also, the rates of evaporation can vary that can cause uneven drying that leads to case hardening, cracking and cellular collapse.